The present invention relates to an apparatus for driving a passenger conveyor in which the operational speed of the passenger conveyor is variable.
A conventional apparatus for driving a passenger conveyor mainly comprises an electric motor, a reduction gear for reducing the rotational speed of the motor to a speed suitable for conveying passengers, and a chain gearing device rotated by the reduction gear to drive a step chain connecting a plurality of steps to each other. The driving apparatus further comprises a means for operating the passenger conveyor at a low speed to variously adjust the passenger conveyor during installation and maintenance thereof.
Such a conventional passenger conveyor provided with the means for operating the conveyor at a low speed is disclosed in Japanese Laid-Open Patent No. 55-101581 for example.
In the passenger conveyor driving apparatus of this type, a drive unit for operating the passenger conveyor at a low speed (6 m/min) is disposed in addition to a main drive unit for operating the passenger conveyor at a normal speed (30 m/min or 40 m/min). The passenger conveyor can be operated using the drive unit for low speed operation during installation and maintenance of the passenger conveyor.
In the conventional passenger conveyor mentioned above, not only is it necessary to have a separate drive unit for low speed operation in addition to the main drive machine, it is also necessary to have a transmission device such as an electromagnetic clutch for enabling the drive unit for low speed operation to be connected or disconnected with the reduction gear, thereby increasing the cost of the passenger conveyor driving apparatus while requiring extra space in the machine room in which the drive units etc. are disposed.
Furthermore, in this kind of passenger conveyor, although it is convenient to install and maintain the drive unit for low speed operation, the operational speed of the passenger conveyor cannot be controlled since the speed is constantly fixed at a safe speed such as 6 m/min. Accordingly, it cannot be adjusted to the various operational speeds needed for the operations during installation and maintenance of the passenger conveyor, thereby reducing the efficiency of such operations.
Another conventional apparatus for driving a passenger conveyor is disclosed in Japanese Laid-Open Patent No. 58-47786 for example and is illustrated in FIGS. 1 and 2. A machine room 2 is disposed at the upper end of a main frame 1 of the passenger conveyor. An upper chain gearing device 3 in the vicinity of the machine room 2 and a lower chain gearing device 4 are respectively attached to the upper and lower ends of the main frame 1. A step chain 5 is endlessly wound around the upper and lower chain gearing devices 3 and 4 to endlessly connect a plurality of steps 6 to each other. A drive unit 7 disposed within the machine room 2 comprises an electric motor 8 and a reduction gear 9. The rotary shaft 8a of the electric motor 8 is connected to an input shaft 9a of the reduction gear 9 through a transmission mechanism 10. A drive sprocket 11 connected to an output shaft 9b of the reduction gear 9 is connected to a driven sprocket 3a of the upper chain gearing device 3 through a chain 12 to transmit the rotation of the reduction gear 9 to the upper chain gearing device 3, thereby driving the step chain 5 for moving the steps 6.
The operational speed of the drive unit 7 is constant in general and increases and decreases in the operational speed thereof are determined by the starting torque of the electric motor and the inertia of the system.
Recently, a passenger conveyor in which the operational speed thereof can be switched in two stages has been recently used.
In such a passenger conveyor, the operational speed of a drive unit is changed by switching the number of poles of the electric motor. For example, the number of poles is set to be six at an operational speed of 40 m/min and eight at an operational speed of 30 m/min.
In the drive apparatus in which the operational speed of the passenger conveyor is constantly fixed, although a slow increase or decrease of the operational speed of the passenger conveyor can be performed by disposing a large-sized fly-wheel etc., but this requires that the brake and other devices be made larger and it also makes it difficult to arbitrarily change the operational speed of the passenger conveyor.
In a passenger conveyor in which the operational speed thereof is switched in two stages, when the operational speed is to be changed, the operation of the passenger conveyor must be stopped once and then restarted after the number of poles of the electric motor has been switched to a suitable number of poles. This stopping of the conveyor is inconvenient to the passengers and the consumption of electric power from restarting is large. Further, since the motor is made larger to accommodate the increase in the number of poles of the electric motor, the electric motor cannot be disposed within the main frame in some cases.